In practice, such an apparatus is also called “flash machine”. In said technique, for the manufacture of a stamp plate, in an open-pored foam material, as for instance EVA (ethylene vinyl acetate), a closing of the pores of the open-pored material of the stamp plate blank is caused by means of short exposures (“flash”, in particular of xenon lamps) in those regions where no stamp imprint shall be created. In those regions where a stamp imprint shall be created with the aid of stamping ink permeating through the porous material, however, the pores remain open.
Such a flash stamp is for instance described in EP 1 976 705 E1.
An apparatus for the manufacture of such a flash stamp plate, or more specifically for the manufacture of a printing block on a stamp plate blank made of a porous thermoplastic material, is for instance known from EP 805 745 B1. In said technique, a stamp plate blank is put into an exposure apparatus along with a pattern (stencil) or a mask which has been produced for instance with the aid of a computer and which comprises the desired stamp imprint image. Normally, as a supporting “table” a glass plate is used in the exposure apparatus, against which the unit consisting of the stencil and the stamp plate blank is pressed by means of a pressing element with the aid of a cover lid. Special stamp plate materials for said flash method are for instance also known from EP 810 100 B1.
Regarding the use of the above-mentioned flash apparatus, in practice experience has shown that when a larger number of stamp plate blanks is exposed, i.e. when a corresponding number of finished stamp plates is manufactured according to the flash method, quite rapidly an overheating occurs in the region where the stamp plate blanks are inserted, i.e. in particular of the glass plate support. If it is not noticed, such an overheating can cause that in the regions of the stamp plate where the pores shall remain open, already an unintentional closing of pores is effected simply in consequence of the insertion and compression, i.e. the closing of the lid, namely by the hot glass support, wherein, moreover, such a partial closing of the pores may perhaps not be noticed so that unsuitable stamp plates are produced. In the more favorable case, when such overheatings are noticed, adverse waiting times are necessary in order to allow the apparatus or its relevant parts to cool down again, which is time-consuming and makes the manufacturing of a series of stamp plates more complicated.